OTTAWA -- As a former journalist, Sen. Mike Duffy knows the components of a story -- you need the who, the what, the where, the when, the why and the how.

In the 61 days an Ottawa courtroom heard evidence on the 31 charges of fraud, breach of trust and bribery the senator is facing, the Crown and the defence argued the first five points.

But with the start of closing arguments on Monday, both sides will now get to the final element so necessary to their respective sides of the case, says Peter Sankoff, a law professor at the University of Alberta.

"It's about the how -- how does all this stuff add up to guilt or innocence," he said.

Duffy, 69, has pleaded not guilty to all charges.

The closing submissions cap off a trial that began in April and was initially supposed to last just eight weeks. But it's a story that starts back in 2008, when the popular broadcaster was appointed by former prime minister Stephen Harper as a Conservative senator for P.E.I.

Four years later, questions about whether Duffy could justifiably claim to be a resident of that province began to surface and from those, more questions emerged about his expenses and living claims.

He'd eventually publicly admit to confusion with the rules and pay $90,000 back into the public purse -- money it would later emerge was not his, but came from Harper's former chief of staff, Nigel Wright. More questions would emerge, this time about the partisan work Duffy was doing and whether taxpayers should have been footing the bill for that, too, as he was billing the Senate for some of those trips.

The whos and wheres and whens and whats of his expenses were the meat of the weeks of testimony that dragged on far longer than anyone expected, including through the early part of the fall election campaign which saw the Conservative government ousted in favour of the Liberals.

There's no question the changing of the political guard in Ottawa took some of the air out of the proceedings, Sankoff noted. But neither side has any room left for it anyway.

"What they were dealing with for long periods, who knew what at what time, who was dealing with the decision, I don't think any of that matters anymore," he said.

"I think they are really going to focus to the extent that they will on trying to explain why he should or shouldn't be convicted."

But that's not to say that Justice Charles Vaillancourt's eventual ruling will have no fallout, Sankoff said.

"What the judge says could have some impact on how the government does business, because the judge could make some statements about the inappropriateness of some of the conduct of the prime minister's office and I think that has resonance even for future governments," he said.

While two weeks have been set aside for the final submissions, the judge has also asked both sides to present them in writing first, in order to focus them in the hope that the full two weeks will not be needed.